Impact of non-pyrethroid insecticide treated durable wall lining on age structure of malaria vectors in Muheza, Tanzania

BMC Research Notes Emidi et al. BMC Res Notes (2017) 10:744 https://doi.org/10.1186/s13104-017-3078-7 Open Access RESEARCH NOTE Impact of non‑pyrethroid insecticide treated durable wall lining on age structure of malaria vectors in Muheza, Tanzania Basiliana Emidi1,2*, William N. Kisinza3 and Franklin W. Mosha1 Abstract Objective: Malaria vectors control interventions are designed to cause immediate killing or shorten mosquito lives, therefore does not allow enough time for the development of the parasites to infective stage. The wall lining is new malaria vectors control intervention in Tanzania where its impact on age structure is not well known. Therefore this study aimed at determining the impact of non-pyrethroid durable wall lining on the age structure of malaria vectors. Results: Higher proportions of An. gambiae sensu lato (57.1%, z = 2.66, P = 0.0077) and An. funestus (64.8%, z = 3.38, P = 0.001) were collected in the control clusters. Unexpectedly, significantly higher proportion of parous An. gambiae s. l. were collected in the intervention clusters (z = − 2.78, P = 0.0054). The wall lining intervention has demonstrated low impact on age structure of An. gambiae s. l., this call for further studies on the efficacy of the intervention. Keywords: Non-pyrethroid treated durable wall liners, Age structure, Parous, Nulliparous, An. funestus, An. gambiae s. l., Malaria vectors, Muheza, Tanzania Introduction Mosquito biting behaviour changes have been reported to be induced by vector control interventions, particularly when excito-repellent insecticides are used [1]. Spraying the walls and ceiling of houses with residual insecticides tends to reduce the survival of mosquito vectors, therefore reduce malaria transmission [2]. This is because, insecticides irritancy cause high proportion of mosquitoes to exit from treated houses. However, treated walls also contribute to decreased feeding rate and resting behaviour of indoor biting mosquitoes [3]. An. gambiae s. s. and An. funestus, which are the malaria vectors, naturally prefer to feed and rests indoors [3–5]. This is in contrast to the strongly exophilic and exophagic; An. arabiensis [6, 7]. Nevertheless, the use of indoor chemical interventions such as long lasting insecticide treated nets (LLINs) and indoor residue spray (IRS) have reported to drive malaria vectors to feed and rest outdoors resulting in a reproductive advantage for them [4]. Such shifting *Correspondence: 1 Kilimanjaro Christian Medical University College, P.O. Box 2240, Moshi, Tanzania Full list of author information is available at the end of the article would also be accompanied by feeding more outdoors at dusk or dawn rather than indoors at mid-night [4, 7, 8]. Outdoor biting mosquitoes remain as secondary sources of malaria transmission as they respond poorly to indoors insecticidal interventions [9–11]. Age grading technique is applied for establishing the parous rate of mosquito populations in order to estimate longevity [12]. Normally, mosquitoes are dissected to observe ovarian dilations in order to determine the proportions that are nulliparous (have not laid eggs) or young mosquito and parous (have laid eggs) or old mosquitoes [12, 13]. Parous mosquitoes are those that have taken a blood meal and oviposited at least once [14]. Age grading in malaria vector is important in estimating the risk of malaria in a particular area [15], with respect to the presence of interventions [16]. Currently, a novel non-pyrethroid insecticide treated durable wall liner (ITWL) which works similar to IRS has been developed. It consists of a thin sheet of cloth made from high-density polypropylene treated with a mixture of two non-pyrethroid insecticides namely; abamectin and fenpyroximate [17, 18]. The impact of ITWL intervention on age structure of malaria vectors is not well known in Tanzania. © The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/ publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Emidi et al. BMC Res Notes (2017) 10:744 Therefore, the present study aimed at determining its impact on age structure of malaria vectors under field conditions in the study area. Main text Materials and methods Study area This cross-sectional study was conducted for the duration of 7 months from November, 2015 to May, 2016 in 18 clusters in Muheza district, North-eastern coast of Tanzania. In recent years, there have been fluctuations in the rainfall patterns with long drought periods in the study area. During implementation of this study, there were long dry seasons which accompanied with dryness of the mosquito breeding sites [19]. The district covers a geographical area of 4922 km2, lying between 5°S latitude and 39°E longitude. The climate is tropical, with dense rainforest over the Usambara mountain ranges and has an annual rainfall of 1000–2000 mm. Muheza district is mainly inhabited by subsistence farmers. Administratively, Muheza district is divided into six divisions comprised of 35 wards with 175 villages [20]. The area is endemic for malaria and lymphatic filariasis whereby An. gambiae s. l. and An. funestus are the main vectors of these diseases [21, 22]. An. gambiae s. l. in this area has also been documented to be resistant to pyrethroid insecticides [23, 24]. Site selection and mosquito collection A total of 18 clusters were selected; nine in control clusters and nine in intervention clusters from clusters in a randomized field trial [18]. Intervention clusters were those with high percentage (over 80%) coverage of Fig. 1 Mosquito trapping. a House type. b Exit trap set on the window Page 2 of 5 durable wall liners installation and they were provided with LLINs while control clusters were the ones which were provided with LLINs alone. The core area of each cluster had a minimum of 124 households [18]. In each cluster, four houses with open eaves and unscreened windows were selected. In each selected house only one window of the sleeping room was chosen for setting exit traps as described in the WHO [12] in order to collect mosquitoes (Figs. 1, 2). Data analysis Data were entered in excel database and transferred to Stata version 13 statistical software where a Two-sample test for proportions (z) was performed. The outcomes of interest were the proportions of parous and nulliparous among the malaria vector species and intervention arms. In all analysis a P value of < 0.05 was considered statistically significant. Mosquito identification and di (...truncated)